Scientists found that both unusually low and unusually high hemoglobin on a routine blood test were linked to higher dementia risk over the next 15 years
In 2004 and 2005, more than 300,000 South Koreans aged 40 and over went in for a routine national health check. Like most check-ups anywhere, it included a standard blood count, the kind of test that usually gets a quick glance and a “your numbers look fine.” Researchers at Dong-A University in Busan then followed those people through national insurance records for up to 15 years to see who developed dementia. One familiar number on that old lab sheet turned out to matter.
The number was hemoglobin, the protein in red blood cells that carries oxygen. People in the lowest fifth of hemoglobin levels had a 16% higher risk of developing dementia than the group with the lowest dementia rate. People in the highest fifth had a 7% higher risk.
In other words, the link between hemoglobin and dementia was not a straight line. Both ends of the range looked worse than the middle, and the pattern was stronger and more consistent in women than in men.
“A blood test most people already get at a routine check-up may say something about their brain health many years later,” lead researcher Hyun Soo Kim said in a statement.
The idea is not new, and the Korean numbers fit earlier work. A 2019 study of more than 12,000 people in the Netherlands found that people with anemia were more likely to develop dementia, and that unusually high hemoglobin was also linked to higher risk, the same U shape. Other routine blood numbers have shown similar long-range signals, from the ratio of white blood cell types to vitamin B12 levels that doctors usually call normal.
What the new study adds is scale and time. The 316,542 participants came from Korea’s National Health Insurance Service screening cohort, which links each person’s check-up results to every later diagnosis. The researchers split men and women separately into five equal groups by hemoglobin, so each group was compared within its own sex.
The second finding is in the type of dementia. For Alzheimer’s disease, the extra risk sat almost entirely at the low end, with a 14% higher risk in the lowest group. For vascular dementia, which comes from reduced blood flow to the brain, both ends mattered: 19% higher risk at the low end and 18% at the high end.
Low hemoglobin is the hallmark of anemia, which is common in women because of blood loss during menstruation and pregnancy. Very high hemoglobin can reflect smoking, dehydration, lung or heart disease. Either way, the number may be less a cause than a sign of how the whole body is coping.
“The findings do not show that haemoglobin itself causes dementia, but suggest that abnormal haemoglobin levels may be a visible marker of wider physical vulnerability relevant to brain health,” Kim said.
Lindsey Sinclair of the University of Southampton, who was not involved, said in a comment released with the study that physical health and brain health are increasingly seen as intertwined, but that more work is needed to see whether the link holds in people from a wider range of backgrounds.
If your last blood test flagged low or high hemoglobin, that is worth a conversation with your doctor in its own right, since it can point to problems that deserve attention. Kim was explicit that the study is not a reason to start taking iron supplements to prevent dementia. The paper’s own conclusion is more hopeful, suggesting that correcting anemia may help, but the study did not test that.
There are limits to what this shows. The study is observational, so it shows a link, not a cause. Dementia can begin years before it is diagnosed, and the early disease may itself affect appetite, weight and nutrition, which could lower hemoglobin rather than the other way around.
Hemoglobin was measured once, at the 2004 to 2005 check-up, and dementia diagnoses came from insurance records, which miss people who were never diagnosed. The effects are modest, and the summary does not say how many people in each group developed dementia. All participants were Korean, so the results may differ elsewhere.
Source
Song JH, Kim HJ, Son M, et al. “The association between hemoglobin level and risk of developing dementia.” Journal of Alzheimer’s Disease, 2026.
DOI: 10.1177/13872877261443702
Also cited
Wolters FJ, Zonneveld HI, Licher S, et al. “Hemoglobin and anemia in relation to dementia risk and accompanying changes on brain MRI.” Neurology, 2019.
DOI: 10.1212/WNL.0000000000008003
